I just realized I have this biggish, vaguely-annotated bibliography of almost 400 works on early American and Western American history. It’s neither current nor authoritative and only goes through 2002, but it’s free and might have a hidden gem or two.

You can download the bibliography in EndNote 4 format. (Hey, it’s been a while since I used it.) Or you can browse it online. Some of the entries have additional notes not shown in the HTML.